In her new book, Holly Menino describes a visit to Richmond Park in England, where big, monumentally antlered red deer dominate the meadows. Their deep-throated roars keep their harems in line and intimidate rival stags. Some hinds, however, pay little attention to their stag’s roar but respond instead to the high, whinnying calls of smaller sika deer. Marching to a different drummer, the hinds stray from the fold and produce hybrid offspring with mating calls intermediate between the two species. Scientists are curious to see if this behavior will lead eventually to the evolution of a third species.

Richmond Park is just one of the many stops in this fascinating book about deciphering the mystery of calls. A journalist and onetime music student, Menino wondered about the differences—and similarities—in the vocal utterances that are the “social glue” in our own lives, as well as in those of other organisms. Advances in recording devices in the past 30 years have triggered an explosion of projects that investigate the nature of human and animal sounds, and Menino decided to explore current discoveries and uncertainties in the study of animal communication. “Each animal, including humans like you and me, lives in its own sound universe,” she writes. “It tunes into those sounds that are critical to its existence and essential to the social life that supports its survival. Each voice, including our own, is perfectly adapted to a particular kind of place in the world and to a society.”

Take tungara frogs. In the darkness and pandemonium enveloping a Panamanian swamp, Menino encounters these amphibians, which make sense out of the cacophony created by males of dozens of species that call or, as the great herpetologist Archie Carr put it, “sing about sex.” “They are ‘tuned’ to a particular range of frequencies,” Menino writes, “making a tungara more acutely sensitive to the sounds of another tungara than to the sounds of other frequencies made by a different kind of frog.” A female tungara not only picks out a male of her own kind from the deafening nocturnal chorus but also selects the one call whose components are most pleasing to her ear. She responds, hops to him, and they mate.

Menino goes on to more complex signals. Birdsong across our planet’s temporal regions is performed almost exclusively by males. But in Panama, males and females of the black-bellied wren sing alternately. Menino listens in on the display, not in the field but from high-tech recordings played back to her from the computer of David Logue, a biologist at the University of Puerto Rico who pioneered duetting studies. A female answers the male’s low-pitched opening phrase, and then switches her “soprano” reply on cue when he continues with a different phrase—on and on together, in extended song.

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[audioplayer:31701|align:left|caption:Black-bellied wren duet recorded by David Logue.]

How did duetting get started? How does it help the birds survive? Logue is working to tease out the answers, but singing a duet may assure both birds that they will support each other in a crisis or suggest to an intruder that it faces a united defense.

Logue points out that neotropical migrants nesting in the north must speed their courtship to rear their young and get them back to the tropics before winter sets in. Tropical species lead more stable lives, establishing long-term relationships and, in some cases, more complex mating songs. The black-bellied wren demands a split-second response from his prospective mate, proving she is not an unknown female or a rival male. “I began to hear that the male would switch songs and the female would immediately switch her song,” Logue explains. “It was a code.”

And if she doesn’t get it right? “He attacks,” Logue said, “because he isn’t convinced she’s the female who is his mate.”

Menino visits Africa’s Kalahari Desert to observe the social life of meerkats. They evolved warning calls for their families that not only distinguish the identity of an approaching predator (a hawk from the air, a jackal on foot, a snake lurking nearby) but also the urgency of the threat (“Be careful” or “RUN!”). Menino cautions there are animal liars, too. Some scientists suspect that a male California ground squirrel may sound an alarm only to send his fellows scampering for cover while he is left alone with a potential mate.

Technological advances also permit researchers to follow animals into otherwise inaccessible environments. In a fjord off the St. Lawrence River in Quebec, scientists track belugas in water as deep as 600 feet. These sociable whales use a series of clicks, twitters, and chirps to navigate, find food, and stay together. Researchers lower sensitive hydrophones into the belugas’ midst to begin separating signature voices of individuals through digital sound precision. By photographing each as it surfaces and identifying it by the varied scars and other marks on its body, then trying to match the individuals with the sound print of their voices, researchers may assemble a picture of the belugas’ social structure and find ways to help them survive.

Ultimately the flurry of studies into animal voices might provide insight into our own voices. Have some uses of animal signals been passed on to humans during the incredibly long, tinkering march of evolution? Menino answers that the issue is “the subject of lively scientific speculation. Eventually this speculation may lead to some understanding of what actually happened in the gap between animals and humans.”